The present invention pertains generally to ball bearings, and in particular to an improved cageless ball bearing which is both resistant to foreign particle-induced seizing, and is self cleaning.
Rolling-contact bearings are composed of a rolling element interposed between an inner and outer race. In a cageless ball bearing a number of balls rotate freely between inner and outer circular races, thereby permitting the races to independently rotate with respect to each other. The races are grooved to captively accept the balls. The balls are disposed between the races so that the space between the races is substantially circumferentially filled with balls. In another type of ball bearing, separators, sometimes called cages or retainers, are used to evenly space the balls from each other around the race circumference.
Various ball bearing designs are well known in the art. For example, U.S. Pat. No. 3,425,759 shows a gyromotor bearing in which a plurality of sintered polyamide resin, lubricant-impregnated balls are intercalated between the solid steel balls of the bearing. U.S. Pat. No. 4,500,144 defines a bearing member which includes a series of carbon separators. As the separators wear, the space between the balls increases as is shown in FIG. 13. Notice that the radial angle between balls 14n and 14 is about 80 degrees. U.S. Pat. 5,309,529 discloses a bearing arrangement for a radial bearing in an acceleration-proof gyroscope. U.S. Pat. No. 5,443,317 comprises a rolling bearing having balls of different diameters. The balls have limited movement within a pocket.
A cageless ball bearing is defined as a ball bearing which does not include any form of cage, retainer, or separator to hold the balls apart, but rather a ball bearing in which the balls are free to travel between the inner and outer races in abutting relationship. In a conventional cageless ball bearing, the bearing has a xe2x80x9cfull complementxe2x80x9d of balls. A full complement of balls is defined as the maximum number of balls that will circumferentially fit between the inner and outer races. That is, there is not enough room in which to circumferentially fit another ball. There is however a very small circumferential gap between balls so that the balls are free to move circumferentially around the races, and are also free to rotate within the races. The total circumferential gap between all balls (also defined herein as the xe2x80x9cmaximum circumferential gapxe2x80x9d) is less than the diameter of one ball, and typically accounts for only about a ten degree or less open sector. This is desirable because by having the balls tightly packed and therefore evenly distributed around the circumference of the races, the axial forces exerted upon the bearing are always balanced, thereby resulting in smooth vibration-free performance.
However, because the balls of the conventional cageless ball bearing are tightly packed around the circumference of the bearing, the conventional cageless ball bearing is highly susceptible to seizing or binding when foreign particles such as sand, rock, chips, debris, and the like are encountered. Particles can wedge into and completely fill the small circumferential gaps between adjacent balls and prevent the balls from both moving circumferentially around the races, and from rotating within the races. When this happens the bearing seizes, usually rendering the parent machine inoperable.
It is toward the solution of this seizing problem to which the teachings of the present invention are directed.
The present invention is directed to an improved ball bearing of the cageless variety which avoids the previously mentioned seizure problems of conventional cageless ball bearings. The present invention purposefully abandons the traditional concept of xe2x80x9cbalancingxe2x80x9d the bearing with a full complement of balls, and in so doing achieves the xe2x80x9cunexpected resultxe2x80x9d of dramatically improving performance in a hostile foreign particle environment. In the present invention at least one ball is intentionally removed from a full complement of balls, so that when the remaining balls are placed in abutting relationship, a large maximum circumferential gap exists. By having at least one ball less than a full complement of balls, the resulting gap comprises a circumferential space that is too large for foreign particles to fill and thereby seize the bearing.
The present invention not only mitigates against the effect of foreign particles, but is also self cleaning by effectively purging the foreign particles from the bearing. The present invention has been found extremely useful in swimming pool cleaning devices, where in certain instances the ball bearings can be exposed to large amounts of sand and other debris which often results in bearing seizure. By using the design of the present however, the bearings were found not to seize when exposed to substantial amounts of sand and debris. It may be appreciated that while the swimming pool application is useful, the principles of the present invention could also be practiced in any environment where foreign particles and/or debris are existent and free to enter the bearing, such as in a windy desert setting.
In accordance with a preferred embodiment of the invention, a cageless ball bearing has at least one ball less than a full complement of balls. That is, the number of balls is at least one less than a maximum number of balls that will circumferentially fit in the space between the inner and outer races.
In accordance with an important aspect of the invention, a cageless ball bearing includes a maximum circumferential gap which subtends an angle of between about 15xc2x0 and about 90xc2x0.
In accordance with an important feature of the invention, the angle is between about 50xc2x0 and about 60xc2x0.
Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.